seems a negative value has to be returned when not valid

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@18744 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/add-ons/kernel/file_systems/dos/dosfs.c

@@ -572,39 +572,39 @@ dosfs_identify_partition(int fd, partition_data *partition, void **_cookie)
 	
 	// read in the boot sector
 	if (read_pos(fd, 0, (void*)buf, 512) != 512) {
-		return 0.0f;
+		return -1;
 	}
 
 	// only check boot signature on hard disks to account for broken mtools
 	// behavior
 	if (((buf[0x1fe] != 0x55) || (buf[0x1ff] != 0xaa)) && (buf[0x15] == 0xf8))
-		return 0.0f;
+		return -1;
 	if (!memcmp(buf+3, "NTFS    ", 8) || !memcmp(buf+3, "HPFS    ", 8)) {
-		return 0.0f;
+		return -1;
 	}
 
 	// first fill in the universal fields from the bpb
 	bytes_per_sector = read16(buf,0xb);
 	if ((bytes_per_sector != 0x200) && (bytes_per_sector != 0x400) && (bytes_per_sector != 0x800)) {
-		return 0.0f;
+		return -1;
 	}
 
 	sectors_per_cluster = i = buf[0xd];
 	if ((i != 1) && (i != 2) && (i != 4) && (i != 8) &&
 		(i != 0x10) && (i != 0x20) && (i != 0x40) && (i != 0x80)) {
-		return 0.0f;
+		return -1;
 	}
 
 	reserved_sectors = read16(buf,0xe);
 
 	fat_count = buf[0x10];
 	if ((fat_count == 0) || (fat_count > 8)) {
-		return 0.0f;
+		return -1;
 	}
 
 	// check media descriptor versus known types
 	if ((buf[0x15] != 0xF0) && (buf[0x15] < 0xf8)) {
-		return 0.0f;
+		return -1;
 	}
 
 	strcpy(name, "no name    ");
@@ -626,7 +626,7 @@ dosfs_identify_partition(int fd, partition_data *partition, void **_cookie)
 	
 	cookie = (identify_cookie *)malloc(sizeof(identify_cookie));
 	if (!cookie)
-		return 0.0f;
+		return -1;
 
 	cookie->bytes_per_sector = bytes_per_sector;
 	cookie->total_sectors = total_sectors;